This invention relates to apparatus for transferring or delivery to an output terminal an electrical charge which is proportional to an electrical charge received on an input terminal.
Electrical charge transfer circuitry has application when it is necessary to measure or respond to electrical charges, and it is convenient or necessary to transfer such charges from one location to another with accuracy. Examples of such applications are capacitive position sensors, piezo-electric sensors, capacitive humidity sensors, electrostatic digitizing tablets, electrostatic field receivers, etc.
An exemplary prior art electrical charge transfer circuit is shown in FIG. 1 to include a capacitor feedback charge amplifier A.sub.1 having an input for receiving an input charge Q.sub.in which is to be "transferred". A capacitor C.sub.g is shown coupled between the input of the amplifier A.sub.1 and ground potential, to represent stray capacitance. A feedback capacitor C.sub.f is located between the output of the amplifier A.sub.1 and the input thereof, and is in parallel with a switch S.sub.i. The output of the amplifier A.sub.1 is coupled via an output capacitor C.sub.0 to an output load, in this case shown to be a voltage source V.sub.1. This electrical charge transfer circuit is well known and widely used.
With the prior art charge transfer circuit of FIG. 1, an error in the output charge may be introduced if the output voltage varies which could occur if the output charge is being accumulated (integrated) on a capacitor. Also, a feedback capacitor is required in the prior art circuit and this dictates that certain integrated circuit fabrication processes must be used to fabricate the circuit. Such processes are typically more expensive and troublesome than if the feedback capacitor did not have to be fabricated with the circuit.